Referring to FIG. 1, a comminution machine, which may also be referred to as a shredder or a mineral reducer, typically includes at least one shaft of polygonal (as illustrated) or keyed section to transmit high torque at low speed mounted by bearings 6 on a frame 10 and driven by a reduction gearbox 8 or hydraulic motor. The frame 10 has two vertical side walls and two vertical end walls which together form a rectangular shape having the top and bottom open. Cleaners 9 (FIG. 3) are fixed to the frame 10 and project into the operating chamber between blades 2 which are separated by spacers 5 on each shaft 1 and arranged helically on the shaft. The blades 2 on one shaft are interleaved with the blades 2 on the other shaft and a minimum clearance exists between the adjacent blades (or a minimum clearance exists between the blades and fixed anvils if only one shaft is used) to produce the cutting action. When two shafts are used, they are rotated in opposite directions. The shafts may be either rotated in synchronization with one another (e.g., so that adjacent teeth on opposite shafts cross an imaginary line between the axes of their respective shafts at approximately the same time), which is preferred since it results in more efficient reduction, or not. Typical prior art comminuting machines are disclosed in patents such as U.S. Pat. Nos. 4,125,228, 4,733,828, 5,799,884, 5,904,305 and 5,992,777, U.K. Patent Application Publication No. 2,322,310 and International Patent Publication No. WO83/02071.
Typical comminution machines allow material to enter at the top of the frame and be processed through the system and discharged through the bottom. The machine may be used for reducing tires, carpet, mattresses, plastic, glass, wood, asphalt or concrete, even concrete with rebar. As such, the blades are subjected to great forces and accordingly to intense wear. Therefore, the blades are typically made by attaching replaceable teeth and wear plates to tooth carriers, with the tooth carriers having a hole in the center which mates with the polygonal (or keyed) shape of the drive shaft so that the tooth carriers are driven by the drive shaft. The number of teeth on each tooth carrier is dependent upon the material being processed and the final size required. It is therefore desirable to have a blade which can be easily adapted to comminute different types of materials.
In a typical prior design, e.g., GB 2 332 310 A, the tooth/blade assemblies were generally circular in shape, with the teeth being mounted in general on the periphery of a cylinder. The surface of the cylinder upstream of each tooth limited the radial depth of the gullet in front of the tooth, and also limited the maximum width of the nip between facing teeth as the teeth approached one another. As a result, the size of the pieces which could be reduced was limited. Another result is that such machines were best suited for minerals not containing ferrous, as opposed to concrete with rebar and/or cable. Such machines worked for smaller materials, such as bricks, but did not work well for larger materials such as larger pieces of concrete or concrete containing rebar and/or cable.
Also, in prior designs, the teeth and wear plates have been attached to the carriers using nuts and bolts. A problem with these attachment systems is that fine particles of the material being comminuted becomes trapped in the threads, making it difficult to replace the teeth and wear plates. The present invention is also directed at a solution to this problem.